1. Field of the Invention
This invention relates to thrust bearing assemblies and more particularly to reversible thrust bearing assemblies of the pivoted pad type.
2. Description of the Prior Art
Large thrust bearings are usually of the type in which a thrust collar on a shaft is supported on a plurality of segmental bearing pads which are pivotally mounted to permit the pads to tilt slightly to establish a wedge-shaped oil film during operation. Long established practice requires that the bearing surface of the shoes remain planar and the pivot be circumferentially offset from the radial centerline of the thrust bearing pad. When a shaft is supported by a pivoted pad thrust bearing, the offset pivot is hydrodynamically correct for only one direction of rotation. If multi-direction shaft rotation is a design necessity such as for pump-storage generator applications, an alternative to plane, pivoted pad thrust bearing pads is required.
One proposed solution is disclosed in U.S. Pat. No. 3,784,266, where a system of grooves in the bearing pads can be selectively supplied with pressurized lubricating fluid causing a simulated offset support for centrally supported bearing pads. A further alternative is provided in U.S. Pat. No. 3,398,996 which illustrates a centrally pivoted bearing pad having two servo mechanisms which simulate the tilting bearing pad configuration for either direction of shaft rotation. Both of the aforementioned patents require building and maintaining additional lubricating systems and activating mechanisms. In addition, if the simulating or servo mechanisms have a short life, bearing life will also be decreased requiring downtime for repair. Thus, centrally pivoted thrust bearing pads are desirable for multi-direction shaft rotation, but improvement in the hydrodynamic characteristics of such a bearing is essential to prolong bearing life and enhance load carrying capacity.